The relationship of certain peripheral sense organs to the cytoarchitecture of the face area of the somatosensory neocortex is distinct and constant in the mouse. Each vibrissa is related to a distinct cytoarchitectonic feature located in layer IV of Sl neocortex, the "barrel". Becuase of the clarity and constancy of this relationship, the cortex of mice will be used as a model in which to precisely determine neuronal organization and connectivity, as well as cortical development. The objectives are five fold: (1) To characterize the neuronal population comprising the cortical barrel by a qualitative and quantitative analysis of the cortex in Nissl, Golgi and Em preparations; (2) To determine the connectivity within and without the barrel from the preceeding analysis and by series of experimental studies. Some brains will be examined autoradiographically for transport of labelled protein to axon terminals following local injections of H3-leucine and proline; others will be examined in the Em following lesions; (3) To examine the alterations in development of the barrels following early lesions to the peripheral vibrissae; (4) To study genetically different strains of mice to determine how alterations in the sensory periphery or in the development of the CNS can affect the appearance of the barrels; and, (5) by comparative studies, using a variety of mammalian forms to determine the extent to which barrels are a general feature of mammalian neocortical organization and to try to relate the appearance of barrels to various patterns of behavior.